Space cooling systems, including both refrigeration and comfort cooling systems, typically include one or more evaporators in heat exchange relationship with the space to be cooled, a condenser external to the space, a compressor for circulating a heat transfer medium, such as a vapor compression refrigerant, between the evaporator and the condenser, and an expansion valve located between the condenser outlet and the inlet to each evaporator. The expansion valve may be positionable at various intermediate positions between a fully open position and a fully closed position to regulate the flow rate of the heat transfer medium through the evaporator. An indoor fan is typically included to provide an airflow across the evaporator and an outdoor fan is provided for cooling the condenser. Conventional space cooling systems also typically include a defrost heater associated with each evaporator, an electro-mechanical defrost timer for selectively activating and deactivating the defrost heater(s), an electrically operable solenoid valve upstream of the expansion valve, and various temperature and pressure sensors for measuring selected temperature and pressure parameters.
Modern-day space cooling systems may also include a microcomputer programmed to control operation of the system based on inputs from various temperature and pressure sensors. Each expansion valve may be controlled in response to the measured temperature differential across the corresponding evaporator. This temperature differential is commonly referred to as the evaporator superheat. Various techniques for controlling the expansion valve in response to evaporator superheat are set forth in U.S. Pat. Nos. 4,067,203; 4,523,435; 4,617,804; 4,620,424; 4,674,292; and 4,787,213.
If one or more evaporators are added or removed from the system, the controller must be re-programmed to control the expansion valves associated with the respective evaporators. Alternatively, a separate controller may be provided for each expansion valve such that each controller is operated separately from the other controllers. In that case, each controller must be configured to receive inputs from all of the system's temperature and pressure sensors.
There is therefore a need for integrated control of a space cooling system and in particular a space cooling system having plural evaporators and expansion valves.